In typical motor vehicle operations, the vehicle engine must drive many auxiliary systems in addition to providing power to the power train which eventually drives the propelling wheels of the vehicle. For example, with water cooled engines, a water pump is connected by a belt or chain drive to the engine crankshaft. Additionally, the engine oil lubrication system pump is driven directly from the vehicle engine. Further, an electric power generator is powered by the engine with a chain or belt drive connection to the engine crankshaft. Other auxiliary systems that are powered by the vehicle engine include ABS braking systems, air conditioner compressors, and windshield wiper driver motor systems and other auxiliary systems.
The driving connection of these auxiliary systems to the vehicle engine, all require some type of mechanical drive train connection between the engine crankshaft and the auxiliary system pump or motor. Each of these drive trains involve energy losses in the engine and units of the drive trains and also provide for the transfer of torque, pulsations, and vibration, between the engine and the auxiliary system pump(s) or motor(s) being driven thereby. Such torque, vibration, and noise transfer in the drive trains between the engine and the auxiliary systems may result in bearing wear problems and generate vibrations which are transferred not only to the engine and the auxiliary systems, but also to the vehicle frame, causing vehicle noise problems, as well as wear problems on the entire vehicle system. Furthermore, since the auxiliary systems operate with varying load demands on the engine such as caused by the switching on and off of a vehicle air conditioning compressor drive motor in response to the air conditioning needs of the vehicle, there are frequently occurring transient start-up and shut-down phases for each of the auxiliary systems, which when they coincide with one another, cause major fluctuations in required engine torque as well as in torque feedback to the engine from the auxiliary systems.
Furthermore, the varying loads imposed by the operation of the auxiliary systems necessarily require varying engine torque output demands on the engine, thereby requiring the engine to operate over a range of different speed and torque values. Optimum engine efficiency may be realistically designed for only a very narrow engine speed and torque range. Such fluctuating loads inherently adversely affect the vehicle engine operating efficiency due to the requirement to design the engine to operate over wide engine speed and torque ranges.